Conventionally, in saddle ride type four-wheel vehicles (e.g., All terrain Vehicle or “ATV”), the vehicle body and the fuel tank and the like are appropriately covered with a resin-made vehicle body cover. For enhancing the workability at the time of maintenance, some of such vehicles are so configured that the fuel tank and the like can be easily detached without removing the vehicle body cover. Such is disclosed, for instance in Japanese Patent Laid-open No. Hei 11-198882.
In the case of a saddle ride type four-wheel vehicle adopting an electronic control type fuel injection system in a fuel supply system, if the piping between the fuel tank and the fuel pump or the like is simplified, the detachment and mounting of these components are facilitated. Particularly, in the fuel pump for supplying the fuel to a throttle body, the layout must be synthetically investigated, taking into account the influences of external forces due to, for example, contact with an obstacle, cooling performance, and the like. In addition, in the fuel tank and the fuel pump, a structure and a layout such that the gathering or capturing (e.g., entrainment) of air into fuel supply system component parts due to variations of the fuel level can be restrained are desirable, in sufficient consideration of behaviors of the vehicle body at the time of traveling on off-road terrain or the like.
In addition, the present invention aims at providing a saddle ride type four-wheel vehicle which enables efficient layout of fuel supply system component parts including a fuel pump and which restrains entrainment of air into the fuel supply system component parts.
A fuel supply system in which a fuel pump is provided in a fuel tank mounted on a vehicle has also been known. Such is disclosed, for instance, in Japanese Patent Laid-open No. Hei 11-93794.
FIG. 23 is a sectional view of the fuel supply system according to the related art. In FIG. 23, a fuel tank 100 has a flat portion 102 in the vicinity of the rear end (the right side in the figure) of a bottom plate 101, and a fuel pump assembly 103 is mounted to the flat portion 102. A fuel pump 104 and a filter 106 connected to a suction port 105 of the fuel pump 104 are disposed on the side of the upper surface of the flat portion 102, i.e., on the side of the inside surface of the fuel tank 100. A discharge-side hose joint 107 connected to a fuel injection valve (not shown) and a retum-side hose joint 108 are provided on the lower surface of the flat portion 102, i.e., on the outside surface of the fuel tank 100.
A fuel supply system having a fuel pump mounted to a bottom plate of a rear portion of a fuel tank in which a front step surface wall for stopping waves is provided for inhibiting a small amount of the residual fuel from moving toward the fuel tank front side at the time of deceleration, at the time of running on a descending slope or at other similar times has also been known. Such is disclosed, for instance, in Japanese Patent Laid-open No. 2003-214274.
Accordingly, the positional relationship between the upper surface of the fuel contained in the fuel tank, i.e., the fuel level, and the fuel pump 104 varies depending on the inclination of the vehicle. In FIG. 23, the fuel level at the time when the vehicle is inclined rearward is indicated by line 109, and the fuel level at the time when the vehicle is inclined forwards is indicated by line 110. As understood from this example, the fuel pump 104 is exposed from the fuel level when the vehicle is inclined forwards. Namely, when the vehicle is inclined forwards, the filter 106 is located on the upper side relative to line 110 indicating the fuel level.
In addition, in the system described in Japanese Patent Laid-open No. 2003-214274, the front step surface wall is provided for stopping waves, which is advantageous concerning the inclination of the vehicle, but the structure inside the fuel tank is thereby complicated. Thus, in conventional fuel supply systems, the fuel pick up condition differs depending on the inclination of the vehicle. Particularly, in an ATV frequently run in an inclined condition on off-road terrain, a system capable of stably supplying the fuel until the residual fuel amount is as small as possible is desired.
Therefore, it is an object of the present invention to provide a fuel supply system for a vehicle which is little influenced by the inclination direction of the vehicle and by which the fuel can be stably supplied to the engine.
Among motorcycles, a saddle ride type vehicle wherein a fuel tank and a saddle ride type seat are disposed at a front position and a rear position on the upper side of an engine and in which a secondary air supply system for clarification of an exhaust gas is provided, has also been known. Such is disclosed, for example, in Japanese Patent Laid-open No. 2000-204939, wherein the secondary air supply system is mounted to a down frame disposed on the front side of the engine inclined forwards and is connected to an exhaust port of the engine through a short piping.
In the present invention, it is desired to reduce the loss due to ventilation resistance by shortening the piping for the secondary air supply system. In order to enhance the secondary air supply efficiency, it is important to lay out the secondary air supply system so as to minimize the influence thereon of the heat from the engine.
Particularly, in a type of covering the periphery of the engine with a vehicle body cover such as an ATV, it is difficult to achieve such a layout in which cooling by running airflow can be expected as in, for example, a motorcycle.
From the viewpoint of enhancing the appearance of the vehicle body, it is desired to lay out the secondary air supply system in such a place as to minimize the possibility of the system being visually exposed to the exterior. Accordingly, it is an object of the present invention to meet these demands.